The present disclosure relates to an apparatus and a method for operating an Ad-hoc mode in a wireless communication network, and more particularly, to an apparatus and a method for operating an Ad-hoc mode based on a power managing scheme and a neighbor node discovering scheme in a wireless communication network.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the internet of things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The internet of everything (IoE), which is a combination of the IoT technology and the big data processing technology through connection with a cloud server, has emerged.
As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “security technology” have been demanded for IoT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched.
Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. The IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing information technology (IT) and various industrial applications.
Generally, configuring an Ad-hoc network of an Institute of Electrical and Electronics Engineers (IEEE) 802.11 system is a technology for acquiring time synchronization among nodes included in a related network. In the Ad-hoc network of the IEEE 802.11 system, power consumption of the nodes included in the related network changes according to whether it is possible to acquire the time synchronization among the nodes included in the related network.
Meanwhile, a beacon frame signal specified in the IEEE 802.11 system includes time-stamp information indicating time which a network manages. As such, in the IEEE 802.11 system, nodes included in a specific network may acquire time synchronization among the nodes based on time-stamp information included in a beacon frame signal.
Meanwhile, in an infrastructure mode of the IEEE 802.11 system, an access point (AP) periodically transmits a beacon frame signal, and stations (STAs) which are connected to the AP maintain a network connection based on the beacon frame signal which the AP transmits. Here, time at which it is expected that each beacon frame signal will be received will be referred to as ‘target beacon transmission time (TBTT)’.
In an Ad-hoc mode of the IEEE 802.11 system, there is no node which performs an operation like in an AP, so STAs which exist in a related network transmit a beacon frame signal alternately and randomly at each TBTT. In the Ad-hoc mode, each node does not transmit a beacon frame signal any more until the nets TBTT after detecting a beacon frame signal in a related network.
In the IEEE 802.11 system, a technology for detecting whether there is a neighbor node is very important. Specially, in the Ad-hoc network of the IEEE 802.11 system, it is very important for a related node to detect a neighbor node and channel status between the related node and the detected neighbor node in a view of routing and interference control.
As such, in an Ad-hoc network of an IEEE 802.11 system, a beacon frame signal is used for a related node to acquire time synchronization among nodes included in a related network, and detect a neighbor node and channel status between the related node and the detected neighbor node.
A process for transmitting a beacon frame signal in an Ad-hoc network of a conventional IEEE 802.11 system will be described with reference to FIG. 1.
FIG. 1 schematically illustrates a process for transmitting a beacon frame signal in an Ad-hoc network of a conventional IEEE 802.11 system.
Referring to FIG. 1, a beacon frame signal is transmitted every beacon interval. If a plurality of nodes transmit beacon frame signals at the same time, performance degradation may occur due to collision among the beacon frame signals.
An IEEE 802.11 system thus specifies that each node randomly transmits a beacon frame signal. Specifically, each node transmits a beacon frame signal based on, for example, a contention-based scheme. That is, each node waits during time corresponding to random delay, e.g., time D1 upon detecting that it reaches TBTT. Each node does not transmit a beacon frame signal if there is a beacon frame signal which is received during the time D1, and transmits a beacon frame signal if there is no beacon frame signal which is received during the time D1.
In FIG. 1, an STA#22 transmits a beacon frame signal in the first beacon interval, an STA#31 transmits a beacon frame signal in the second beacon interval, and an STA#15 transmits a beacon frame signal in the third beacon interval.
Like this, in an IEEE 802.11 system, each of a plurality of nodes may detect a neighbor node using beacon frame signals which the plurality of nodes transmit randomly and alternately.
In the Ad-hoc mode of the IEEE 802.11 system, all nodes acquire time synchronization using a beacon frame signal and operate corresponding to the acquired time synchronization. If a network including relatively many nodes is configured in a relatively large region, it is difficult for all nodes included in the network to acquire time synchronization.
As a result, in a wireless network in which time synchronization is not acquired, relatively much power is consumed for a related node to discover a neighbor node and detect whether a message will be transmitted to the related node.
A process for transmitting a beacon frame signal in an Ad-hoc network of a conventional IEEE 802.11 system has been described with reference to FIG. 1, and a process for transmitting a training symbol in an Ad-hoc network of a conventional IEEE 802.11 system will be described with reference to FIG. 2.
FIG. 2 schematically illustrates a process for transmitting a training symbol in an Ad-hoc network of a conventional IEEE 802.11 system.
Referring to FIG. 2, it will be noted that a process for transmitting a training symbol in FIG. 2 is a process for transmitting a training symbol in a case that a beacon frame signal includes 12 training symbols.
In the IEEE 802.11 system, a beacon frame includes a preamble field, and the preamble field includes 10 short training symbols and 2 long training symbols. During a time interval corresponding to the 10 short training symbols, each STA detects a signal, and performs an automatic gain control (AGC) operation and a coarse frequency offset estimating operation. During a time interval corresponding to the 2 long training symbols which are transmitted after the time interval corresponding to the 10 short training symbols, each STA performs a refinement frequency offset estimating operation and a channel estimating operation.
The beacon frame includes network information, time stamp, and the like as well as the preamble field.
Meanwhile, in a case that each node randomly transmits a beacon frame signal to acquire time synchronization of a network like in the IEEE 802.11 system, there are many advantages in a view of resource allocation and power management.
However, there may be a case that a direct connection between two nodes within a network is impossible since nodes are located at a relatively large coverage. In this case, it may be difficult for all nodes in the IEEE 802.11 system to acquire time synchronization, this results in increase of power consumption of each node. That is, time which each node operates a receiver for discovering a neighbor node and detecting whether a message is transmitted to each node becomes long.
Further, each node determines whether to randomly transmit a beacon frame signal. In the IEEE 802.11 system, if the number of nodes included in an Ad-hoc network is increased, a plurality of nodes transmit beacon frame signals at the same time, so collision among the beacon frame signals may occur. The collision among the beacon frame signals may make it difficult for the nodes included in the Ad-hoc network to stably receive a beacon frame signal, so this makes it difficult for the nodes to acquire time synchronization to decrease stability of a total system and to increase power consumption of the nodes.
However, the IEEE 802.11 system considers only a case that a relatively small number of nodes are located within a relatively short distance, so an Ad-hoc network which is implemented in the IEEE 802.11 system needs to be implemented as a short range network with a small scale.
Meanwhile, in the IEEE 802.11 system, each node randomly transmits a beacon frame signal to discover a neighbor node and measure channel status between each node and the neighbor node. However, if a service coverage of the Ad-hoc network is implemented as a relatively large service coverage, it is impossible for each node to perform a discovering operation and a channel status measuring operation for all neighbor nodes in the Ad-hoc network.
As described above, in the Ad-hoc network, each node determines whether to randomly transmit a beacon frame signal. If the number of nodes included in the Ad-hoc network of the IEEE 802.11 system is increased, the number of beacon frame transmitting opportunities which are given to each node is decreased. If the number of beacon frame transmitting opportunities which are given to each node is decreased, neighbor nodes which are located around a related node may not discover the related node. In this case, even though the neighbor nodes may discover the related node, the related node may not accurately measure channel status between the related node and the discovered neighbor node.
As such, the IEEE 802.11 system considers only a case that a relatively small number of nodes are located within a relatively short distance due to a case that a neighbor node discovering process and a channel status measuring process may not be normally performed, so an Ad-hoc network which is implemented in the IEEE 802.11 system needs to be implemented as a short range network which has a relatively small service coverage.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.